Let science get your kids—or even just you—into gardening.

Occasionally, we here at Ars like to nerd out about things that aren't smartphones, processors, or dark matter. For a few of us on staff, one of those nerdy pastimes involves the plant biology that is literally right in our backyards. People pick up gardening for numerous reasons, but one reason I got into it was because of the science. There's so much to learn about plant biology when you go hands-on, even at a small scale. I grow a lot of stuff in my Chicago garden, and while not everything is a success, it provides great opportunities to learn and iterate.

But not a lot of people are into gardening, relatively speaking. Or so I thought—when I semi-jokingly tweeted that I would begin making garden posts here on Ars, the response was overwhelmingly positive. So we thought we would experiment with a weekend feature on cloning plants to get things started.

How to root a tomato cutting (aka “clone” a tomato plant)

Tomatoes are some of the most popular fruits to grow at home, and they're my personal favorite as well. Depending on where you live, you might have a long enough growing season to get back-to-back plantings going, and it's not always fun to start from seed. Or you might want to give away some plants to friends and neighbors. You might even have a friend who grows amazing tomatoes and you want one of those for yourself.

Whatever the case, it's extremely easy to grow new tomato plants from cuttings. If you're not familiar, it is exactly what it sounds like—a piece of an existing plant that you cut off. No roots, no nothing. Just a piece of a plant and some dirt.

For the first part of this tutorial, I'm using a two-week-old baby tomato plant as the example. Toward the end, I do the same thing, but with a cutting from an adult plant in order to "clone" it. The process is exactly the same for both, though you may have to be gentler with the young plants versus mature cuttings.

Why might you start with a baby tomato plant that has been cut off? I had to cut this plant from its roots because it was too close to its sibling in the starter cup. (The roots were too intertwined for me to feel comfortable separating them without damaging the one I wanted to keep.) Typically this is just called "thinning," when gardeners go in and cut off all but the best seedling. But sometimes you want to save the ones you're cutting off. Like I said, the process is exactly the same whether you're dealing with baby plants or mature branches.

So you have the cutting (seen above). Some gardeners like to scrape the sides of the stem with a sharp knife or a razor blade in order to stimulate root growth, but it's not required:

I put my root down

At this point, people sometimes like to use rooting hormone. In my experience this is entirely unnecessary for tomato plants—they root so easily, there's no need to spend the money on it. Plus, many commercial rooting hormones contain pesticides, meaning they're not fit for organic gardening. But if you want to use it, you can—there are other plants that don't root so easily, so if you plan to take cuttings from other things, it might be useful.

Commercial rooting hormone contains auxin, which is a naturally occurring hormone that plants also generate themselves. Auxin is key for plants' cell growth; in particular, its presence helps a plant decide when it's time to put out more roots (versus, say, more leaves up top). Synthetic auxin is what you find in the bottle at the garden center. Applying it to a root-less stem or cutting boosts the auxin levels in that area of the plant, essentially telling it to start putting out more roots where it has been applied. (This is a very basic explanation; there are white papers upon white papers about the effects of auxin if you're interested in going down the rabbit hole.)

But tomato plants are already dying to put out new roots along the length of the vine—sometimes, gardeners notice tomatoes trying to put out new roots above ground on their own if the stem is constantly being splashed with water. You can bury a fairly large tomato plant with only the top poking out of the soil, and it will eventually put out roots along the entire length of plant that you buried. Many other plants do not do this—by default, they only put out roots from the original root ball—which is why you might want to use a rooting hormone to help those cuttings put out new roots. If you choose to use rooting hormone with a tomato cutting, though, it usually just means it will put out roots even faster than it would have on its own.

For rooting hormone, there are two kinds: gel and powder. If you're using the gel, you would use something (a knife, or whatever you have) to lightly coat the outside of the cutting. If you're using powder, dip your cutting into some water and then into the powder to coat the stem.

Now, whether you're using rooting hormone or not, stick the stem into a smallish cup filled with soil. (I used compost because that's what I had available, but you could use any garden soil or seed starter mix. I personally do not recommend just using soil from your lawn, although if you did, I'm sure it would work fine.) Make sure there are holes poked in the bottom of the cup—I poke holes in plastic cups using a barbecue skewer. I like to use the translucent cups for cuttings because it lets me know when the plant has finally rooted, but they're not the best choice once you get to growing. We'll get to that later.

The baggie is to help keep moisture in so the plant can continue to live while it works on putting out new roots. Without the baggie, the cutting would lose all of its water through its leaves and die, so this is a necessary step. Within a few hours of doing this (whether with a baby plant or a mature cutting), your cutting will most likely wilt and look like it's about to die:

That's because it's no longer getting water through its roots. During the editing of this piece, one Ars staffer asked why the cutting doesn't just shrivel up and die. As long as it's getting water somehow—in this case, by basically "submerging" the stem in wet soil and making sure it doesn't lose too much water through its leaves—a cutting can stay alive for an almost alarmingly long time. But exposing a root-less stem to water will only work for so long, because it's more difficult to absorb water through its stem than through roots, and it will die eventually without more help. (This is why cut flowers from the flower shop can stay alive and beautiful for days after you purchase them, as long as you keep them in a vase with water. But the vase isn't magical, so they eventually die.)

That's why auxin is important; the plant is generating its own auxin in order to put out new roots so it can stay alive for the long term. Or if you're using rooting hormone, the synthetic auxin is there to help tell the plant "put out roots now!"

Don't worry; as long as you watered your soil and have a bag over the top, the wilted cutting should come back in about a day or so.

Taking a cutting from a mature plant

Here I have a horrible-looking tomato plant that I grew indoors all winter. It's not particularly large—maybe a foot tall at best—and I'm ready to just clone it and start over outside. (See? Easier than starting from seed.)

First, you have to select a good cut. You can do this from the "top" of the plant or from one of the suckers (or side shoots), as long as it's big enough. Keep in mind that it can't just be any old leaf you select from the plant. New growth has baby leaves coming out of it—it's not a leaf itself. I decided to make my cut a few leaves down from the top, like so:

But this piece is huge—it will lose a ton of water through its leaves if I leave it as-is. As such, it's wise to cut off all the bottom leaves and suckers in order to come out with a bare minimum of leaves to survive.

Enlarge/ All trimmed down, except I should have also trimmed those flowers on the left.

Above is the piece I had left after I trimmed everything I wanted to trim. I should have also trimmed those flower buds that you can see on the top left side. By leaving them on, I'm risking this cutting trying to flower and produce tomatoes immediately after it roots, and I don't want that because I want the plant to put its energy into growing bigger first. Luckily, I can cut off those flower buds at any time.

After scraping the sides (like I did above with the 2-week-old seedling), once again stick it into a cup with some soil, water it, and put a baggie over it. For the first day, you may want to put it in a shaded area. After that, put it in a sunny windowsill (but not outside) so it gets some light, but not enough to stress the plant while it's putting out new roots. Make sure to keep the soil moist (but not soaking) during this time.

This is why I like to use translucent cups for rooting cuttings, because it allows me to see when the plant has rooted without me having to constantly remove it from its cup. But if you used opaque cups, that's fine—after a week or so, put your hand over the top of the cup with the stem in between your fingers, turn it upside down, wiggle the cup a bit, and slide the cup off. You should see at least a few roots; if you don't, put it back in and wait a little longer.

Once your cutting has rooted itself, it's basically a new plant. If you're using translucent cups like I am, you'll want to re-pot into something opaque (and preferably larger). Roots can easily die off when exposed to sunlight, so you don't want to continue growing in something that can allow light through. If you're cheap like me, you could pot up into something like a 16oz Solo cup (with holes poked in the bottom) and it would be fine. Or, since it's getting to be nice out already, you could plant your newly rooted tomato plant directly outside, or into its final container that it will grow from.

Science!

There are a number of reasons why this is cool. As I wrote earlier, doing this can speed up the process and remove some of the tediousness (plus lots and lots of failure) of starting your own seeds. It's even cooler, though, because you basically get unlimited free plants out of it—you could take a cutting from a friend or neighbor, or take your own cuttings in order to multiply the plants you're growing in your own garden. If you live in a climate with warm winters like Florida or Mexico, you could take cuttings from your plants that are already finished and dying in order to start new plants for a second growing season. Or if you're like me, you just like making clones for the sake of doing so, because generating independent new plants from existing ones is a fun activity. Kids love it, too.

Again, you can do this with tons of different plants. Roses are a common one (though you should be careful—many rose varieties are now patented, and the companies forbid you from propagating them via cuttings without paying. To them, it's like torrenting an illegal copy of the rose). Herbs like basil and rosemary are also very common; in fact, I find starting rosemary from seed next to impossible, so cuttings are really my only hope.

You can also clone pepper plants, eggplants, grape vines—the list goes on forever. I once took a cutting from my grandmother's hydrangea bush in California, wrapped it in a damp paper towel, put it in a plastic baggie, and flew with it back to Chicago before rooting it at home. The only thing to keep in mind is that some plants take a lot longer than tomatoes to put out new roots—cuttings from woody plants, like roses, can sometimes take months. But once you get the hang of the process, it's kind of addictive to just start trying to root everything.

If posts like this interest you and you'd like to see more, or if you have other garden science questions that you'd like to see answered, please leave your comments in the discussion or shoot me an e-mail directly. In the meantime, if you're interested in learning more about how gardening can change communities, I recommend watching guerrilla gardener Ron Finley's TED talk and then heading outside to, as he put it, "plant some sh*t."

Promoted Comments

You use a sterile razor blade to split the stem in half instead of cutting diagonally. After that you apply the Auxin (i.e. rooting gel / powder) to the site and surround it with wet tissue / light soil wrapped with a plastic bag. After a few days, roots will begin to appear, at which point you can slice off the remaining stem tissue on either side connecting it to the original plant and put it into your new planter.

Because you haven't fully cut the clone from the original plant, the outer stem tissue continues to carry water and nutrients to the leaves of your clone, which means you aren't at risk of killing it through water / nutrient loss. It also lets you ensure that roots are getting well established before transplanting to avoid shock.

In the end, it results in a much healthier clone that 'springs back' to growth more quickly. It works better with sensitive and fragile plants as well.

Another way would be to use Horticultural Vermiculite as the medium that the clone cutting is placed in to root itself. Since its pretty fine you'll find there is less of a chance of roots breaking if you pull the clone out of the Horticultural Vermiculite when ready to plant outside. Or if your one of those people who likes to check for fresh roots. Usually you can take the cut, put it in the HV using distilled/spring water and no rooting agent, cover with a clear plastic baggie or clear lid for a day or two to prevent dehydration. Once you know they can survive w/o the cover, remove it and wait for the roots to show. Misting the leaves here and there as your waiting for the roots.

As others have said, use a sterilized razor blade to make sure you are not transmitting any bacteria. You can also do this under water, preferably distilled/spring water, to prevent air embolisms from forming when making the cut.

I've rooted bell peppers, jalapeños, strawberry, blueberry's, apple tree (with just a leaf!), tomatoes, roses, etc by using water, soil, HV, peat pucks, or perlite methods. Some plants or people seem to prefer or just have a higher success rate with one method over the other. I've used rooting powder and liquids which do help speed up the process but after finding a method that works, they just sit on a shelf now.

The only thing I can say is trial and error, learn from your mistakes as well as others and just keep at it till you find your groove.

Jacqui Cheng
Jacqui is an Editor at Large at Ars Technica, where she has spent the last eight years writing about Apple culture, gadgets, social networking, privacy, and more. Emailjacqui@arstechnica.com//Twitter@eJacqui

Humanity thrived when agricultural knowledge and plants were freely shared. People "torrented" tomatoes, potatoes and everything in between. Now we're restricting it with IP laws - a big step backwards, I think.

How fun to see an article like this on Ars! Thanks for writing it up. I've got a couple tomato plants I've overwintered & re-cloned for the past few seasons, and they're still going strong. I fully agree, once you get the hang of it, it's kind of addictive seeing what you can propagate.

Jacqui, thanks for the nice write-up. I would just like to add that it is advisable to disinfect your cutting tools so that you don't transfer pests or otherwise contaminate your plants. I use Dettol - in the U.S. you might look for Lysol as an alternative.

As someone who has managed to kill Cress (unintentionally) and failed at attempts to grow everything from herbs to tomatoes & peppers in a windowbox, I leave growing food to the experts. Since said experts are practically on my doorstep and in every direction for at least 20 miles, I'm well catered for.

That's not to dismiss the joy of growing your own, most family members of my grandparents generation grew their own vegetables and one was a farmer all his life. It must be very satisfying to eat a meal you grew yourself. Never managed it myself. /sigh

EDIT: I'm encouraged by the article and tips in the comments. Growing from seed is a little ambitious for a beginner like me. Time to try again, this time with a young plant from the local market.

EDITEDIT: It just occurred to me on re-reading, since plastic drinks cups are usually available in the same sizes, you could use an opaque cup to make a light protecting sleeve (cut and discard the base) to cover the transparent cup. In this way your sleeve protects the roots from light and you could slip off the opaque sleeve to check for roots without disturbing the soil. *This might be ingenious, on the other hand I kill Cress without even trying.*

Jacqui: In the Chicago area there are 2 separate indoor commercial farms. You might want to check them out. They offer tours. I was going to check out at least one of them. Both seem to be in the industrial near southwest side of town (Old stockyards area) in old warehouses. One of the places uses red and blue LEDs for light. They also farm tilapia for the plant nutrients.

I'd love to see more stories about gardening as I have been doing so for about three years now. One area of particular interest is that of apartment gardening as I am going to be moving into an apartment and I will have to leave my large plot I have been using for the past couple of years. Also, very informative, starting from seed can be a real pain.

"Roses are a common one (though you should be careful—many rose varieties are now patented, and the companies forbid you from propagating them via cuttings without paying. To them, it's like torrenting an illegal copy of the rose)."

Surely any patent claims on propagating roses would run afoul of first sale. A little more on this topic would be illuminating.

"Roses are a common one (though you should be careful—many rose varieties are now patented, and the companies forbid you from propagating them via cuttings without paying. To them, it's like torrenting an illegal copy of the rose)."

Surely any patent claims on propagating roses would run afoul of first sale. A little more on this topic would be illuminating.

This at least makes an interesting pedagogical device for teaching kids about IP law, and a good talking point when debating the philosophy with them.

An interesting, if somewhat basic article, though I can imagine some medicinal or cash crops would be more practical / profitable than tomatoes for home growers, especially given the pot liberalisation laws in the US recently. I doubt Ars are going to run a 'grow your own weed' series though... ah well.Like MemphisBob I'd be interested in further details of the legal aspects of home horticulture - how can you 'patent' something that is (literally) by nature designed to reproduce itself?I'm vaguely familiar with Monsanto's efforts to prevent commercial 2nd generation use of their 'products', but wasn't aware of similar restrictions on home growers.I'm assuming that this is a US-specific thing - while many countries are signed to the UPOV convention (which originally banned plant patents?) afaik in other countries you can propagate protected varieties by cuttings or even seed (breeders privilige / farmers privilige in the UK).

If your original plant is an heirloom tomato, ignore the rest of this. If it is not, there are technical issues about reproducing hybrids by "cloning". Many hybrid and GMO plant owns patents on their products that preclude any sort of production that doesn't come directly from purchased seed.

I'd love to see something about plant tissue culture. I've got a couple of rare Pelargonion ardens plants which are notoriously difficult to propagate and I've been thinking about trying tissue culture like the big plant nurseries do. You can buy some of the stuff to do this online (hormones, growth gel medium etc.) but I'm not sure I'd know how to begin...

"Jacqui is senior Apple[s] editor at Ars Technica". Amused me anyway. In all seriousness, I enjoyed this article and would be happy to see more in the same vein. I'm sure I remember reading on Ars recently about how most modern tomato cultivars are virtually flavourless. Any thoughts on this and recommendations about which ones we should be growing for good flavour?

One thing I didn't notice mentioned, perhaps because Ars readers are assumed to be more clever, is that in cloning a plant in this manner produces an exact genetic duplicate of the original plant. Saving seeds from your favorite tomato plant can't guarantee that what results will have the same features you desired from your original plant. Cross pollination from other nearby plants can introduce slight genetic changes in the seeds that result.

quote :"Again, you can do this with tons of different plants. Roses are a common one (though you should be careful—many rose varieties are now patented, and the companies forbid you from propagating them via cuttings without paying. To them, it's like torrenting an illegal copy of the rose). Herbs like basil and rosemary are also very common; in fact, I find starting rosemary from seed next to impossible, so cuttings are really my only hope."

if one is cloning the plant, and not making any money of it can they still sue you?... and how does the company prove that the plant in question has been cloned? Are there CSI: plant Investigators? ...

You use a sterile razor blade to split the stem in half instead of cutting diagonally. After that you apply the Auxin (i.e. rooting gel / powder) to the site and surround it with wet tissue / light soil wrapped with a plastic bag. After a few days, roots will begin to appear, at which point you can slice off the remaining stem tissue on either side connecting it to the original plant and put it into your new planter.

Because you haven't fully cut the clone from the original plant, the outer stem tissue continues to carry water and nutrients to the leaves of your clone, which means you aren't at risk of killing it through water / nutrient loss. It also lets you ensure that roots are getting well established before transplanting to avoid shock.

In the end, it results in a much healthier clone that 'springs back' to growth more quickly. It works better with sensitive and fragile plants as well.

This was a great article. I don't know how far we've come as a society when patents can be made for nature. Humans seem to have a need to own everything. Not that there's anything wrong with that, but a line has to be drawn somewhere. Anyway, I look forward to trying this out.

@Jacqui, I'm going to third the questions about plant IP. It seems like going over that more in depth would be spot on Ars material considering the coverage on media and software IP the site does.

I find it absurd vegetables can be patented and that growing roses would be a crime.

Also, considering the homogenization of commercial tomatoes into the bland fruit they now are makes me wonder why anyone would care. The more flavourful varieties are almost exclusively non-Lab oriented. (Didn't Ars have an article about that?)

Another way would be to use Horticultural Vermiculite as the medium that the clone cutting is placed in to root itself. Since its pretty fine you'll find there is less of a chance of roots breaking if you pull the clone out of the Horticultural Vermiculite when ready to plant outside. Or if your one of those people who likes to check for fresh roots. Usually you can take the cut, put it in the HV using distilled/spring water and no rooting agent, cover with a clear plastic baggie or clear lid for a day or two to prevent dehydration. Once you know they can survive w/o the cover, remove it and wait for the roots to show. Misting the leaves here and there as your waiting for the roots.

As others have said, use a sterilized razor blade to make sure you are not transmitting any bacteria. You can also do this under water, preferably distilled/spring water, to prevent air embolisms from forming when making the cut.

I've rooted bell peppers, jalapeños, strawberry, blueberry's, apple tree (with just a leaf!), tomatoes, roses, etc by using water, soil, HV, peat pucks, or perlite methods. Some plants or people seem to prefer or just have a higher success rate with one method over the other. I've used rooting powder and liquids which do help speed up the process but after finding a method that works, they just sit on a shelf now.

The only thing I can say is trial and error, learn from your mistakes as well as others and just keep at it till you find your groove.